In the United States alone nosocomial bacteremia develops in about 194,000 patients, and of these about 75,000 die. Maki, D. C., 1981, Nosocomial Infect., (Dikson, R. E., Ed.), page 183, Yrke Medical Books, U.S.A. Most of these deaths are attributable to six major gram-negative bacilli, and these are Pseudomonas aeruginosa, Escherichia coli, Proteus, Klebsiella, Enterobacter and Serratia. The current treatment for bacteremia is the administration of antibiotics which, unfortunately, have limited effectiveness.
The precise pathology of bacteremia is not completely elucidated, nevertheless, it is known that bacterial endotoxins, lipopolysaccharides (LPS), are the primary causative agent. LPS consist of at least three significant antigenic regions, the lipid A, core polysaccharide, and O-specific polysaccharide. The latter is also referred to as O-specific chain or simply O-antigen. The O-specific chain region is a long-chain polysaccharide built up from repeating polysaccharide units. The number of polysaccharide units differs among different bacterial species and may vary from one to as many as six or seven monosaccharide units. While the O-specific chain varies among different gram-negative bacteria, the lipid A and core polysaccharides are similar if not identical.
Since LPS plays a key role in sepsis, a variety of approaches has been pursued to neutralize its activity. Presently, there is considerable work which suggest that antibody to LPS will soon be a valuable clinical adjunct to the standard antibiotic therapy.
LPS initiates a cascade of biochemical events that eventually causes the death of the patient. It is widely believed that the second event, after the introduction of LPS, is the production of tumor necrosis factor (TNF) as a result of LPS stimulation of macrophage cells. Thus, considerable effort has been expended to produce neutralizing antibody to TNF, or other molecules that could inhibit its septic effects. It is likely that antibody to TNF will have valuable clinical applications. Tracey, et al., 1987, Nature, 330:662.
TNF has been shown to exist in both membrane bound and soluble secreted forms. Decker, et al., 1987, J. of Immunol., 138:957; Kriegler, et al., 1988, Cell, 53:45. Human TNF has been cloned and shown to consist of a 17 kD polypeptide, plus an unusually long 76 amino acid putative signal leader sequence. The 17 kD molecule is a key agent involved in initiating the biochemical cascade responsible for sepsis. It has been proposed by Kriegler, et al., 1988, Cell, 53:45, that TNF may exist as both a membrane bound 26 kD form, and a soluble form corresponding to the 17 kD species. The 26 kD form is the precursor, or prohormone, of the mature 17 kD molecule. It has further been proposed by Kriegler, et al. above, that the two forms of TNF may have different biological effects.
It will be appreciated that because TNF plays a key role in causing sepsis that there is a need to identify and develop anti-TNF prophylactics/therapeutics. As mentioned above, anti-TNF antibody appears to be promising, and has been shown to be effective in baboons. However, these studies have involved the use of non-human TNF and non-human TNF antibody. From a practical standpoint non-human anti-TNF antibody will have limited therapeutic application because of immunologic rejection of the antibody by a patient's immune system. Consequently, human antibody, or genetically engineered antibody consisting of the human constant region and the mouse variable region are preferred.
TNF, in addition to playing a critical role in sepsis, has recently been shown to be involved in initiating the expression of human immunodeficiency virus in human cells that carry latent virus. Folks et al., 1989, PNAS (USA), 86:2365. Thus, preventing or inhibiting the formation of the 17 kD, or lower molecular weight forms of TNF would be a valuable prophylactic for the treatment of AIDS patients by preventing the expression of virus that is latent in the patient.
TNF also plays a role in various autoimmune diseases, particularly arthritis. Duff, et al., 1987, International Conference on Tumor Necrosis Factor and Related Cytotoxins, 175:10. Thus, compounds or methods for inhibiting TNF action will have considerable application for the treatment of a variety of diseases of immunologic origin.
In addition to antibody, other molecules with TNF inhibitory activity are being sought. Non-antibody TNF inhibitors are described by Seckinger, et al., 1988, J. Exp. Med., 167:1511, and Seckinger, et al. 1989, J. Biol. Chem., 264:11966, and in EPA 88830365.8, inventors Wallach, et al. The inhibitors are present in the urine of febrile patients, and have been purified and shown to have molecular weights of about 27,000-33,000. To date neither of the inhibitors have been shown to be effective in the treatment of sepsis.
From the foregoing discussion it is apparent that there is a need to identify and develop additional anti-TNF inhibitors, both antibody based or otherwise, that may be efficaciously applied in the treatment of sepsis.
In addition to TNF, IL-1 is thought to be involved in sepsis, and furthermore is believed to have multiple biological activities with the two most prominent being fever production and lymphocyte activation. For instance, IL-1 interaction with endothelial cells has been shown to enhance procoagulant activity and endothelial cell adhesiveness for leukocytes. Also, as a consequence of endotoxin exposure, IL-1 is thought to induce an inhibitor of tissue plasminogen activator which would exasperate the coagulation events occurring during an acute inflammatory reaction. Finally, IL-1 is thought to cause the production of platelet activating factor and arachidonic acid metabolites, both of which are involved in an organism's response to endotoxin. It is worth noting that platelet activating factor and arachidonic acid metabolites are also directly produced in response to endotoxin.
There are two forms of IL-1:IL-1 .alpha. and IL-1 .beta.. Although these molecules share limited sequence homology they have similar biological activity. Dinarello, C. A., et al., 1986, Journal Clinical Invest., 77:1734. Both molecules have molecular weights of about 17.5 kD, and are produced from a precursor molecule with a molecular weight of about 31 kD.
Because IL-1 has pleiotropic biological activities, many of which adversely affect the organism, it would be expected that the molecule must be tightly regulated if it is not to be injurious. Indeed, there are several reports of IL-1 inhibitors that regulate the action of IL-1. IL-1 inhibitory activity has been reported in monocyte conditioned medium, wherein the monocytes are grown on adherent immune complexes. Arena, W. P., et al., 1985, Journal of Immun., 134:3868. Additionally, an inhibitor has been reported to be present in urine. Seckinger, P., et al., 1987, Journal of Immun., 139:1546. Lastly, a protein inhibitor, purified and cloned, that has interleukin-1 receptor antagonist activity has been reported. Hannum, et al., 1990, Nature, 343:336, and Eisenberg, S., et al., 1990, Nature, 343:341.
It is thus becoming apparent that aside from their normal biological functions, which have not been fully elucidated, cytokines are pathologically associated with systemic changes arising from infection and tissue injury as witnessed by the fact that TNF and IL-1, alone or in combination, can cause a shock state in animals that hemodynamically and hematologically is characteristic of septic shock in man caused by bacterial infection. Further, TNF and IL-1 also play a role in various autoimmune diseases, particularly arthritis. Duff, et al, 1987, International Conference on Tumor Necrosis Factor and Related Cytotoxins, 175:10. No doubt these and other cytokines will be found to play a role in diseases other than those mentioned above. Thus, it is highly desirable to identify inhibitors of the cytokines that can be used to control their undesirable biological effects.